FIG. 1 shows a detail of a connecting rod of an internal combustion engine with an adjustable compression ratio, as known from DE 10 2010 016 037 A1. FIG. 1 illustrates a connecting rod 10 having a crank pin bearing eye 11 and a piston pin bearing eye 12, wherein the crank pin bearing eye 11 serves to connect the connecting rod 10 with a crankshaft not illustrated in FIG. 1, and the piston pin bearing eye 12 serves to connect the connecting rod 10 with a cylinder piston of the internal combustion engine, which piston is not illustrated in FIG. 1. The connecting rod 10 has an eccentric adjustment mechanism assigned thereto, which comprises an eccentric body 14 and eccentric rods 15, 16. The eccentric body 14 has a piston pin bore arranged eccentrically with respect to a centre 17 of the piston pin bearing eye 12 and having a centre 18, the piston pin bore receiving a piston pin. The eccentric adjustment mechanism 13 serves to adjust the effective connecting rod length leff, wherein the connecting rod length is defined as the distance of the centre 18 of the piston pin bore to a centre 19 of the crank pin bearing eye 11. For turning the eccentric body 14 and thus for changing the effective connecting rod length leff, the eccentric rods 15, 16 of the eccentric adjustment mechanism 13 are adapted to be displaced. Each eccentric rod 15 has a piston 20 and 21, respectively, assigned thereto which is slidably supported or guided in a hydraulic chamber 22 and 23, respectively.
A hydraulic pressure prevails in the hydraulic chambers 22, 23 that acts on the pistons 20 and 21 respectively assigned to the eccentric rods 15, 16, wherein a shifting of the eccentric rods is possible or not possible in dependence on the quantity of oil in the hydraulic chambers 22, 23.
The adjustment of the eccentric adjustment mechanism 13 is initiated by the action of mass and load forces of the internal combustion engine, which act on the eccentric adjustment mechanism 13 during a duty cycle of the internal combustion engine. During one duty cycle, the directions of action of the forces acting on the eccentric adjustment mechanism 13 are constantly changing. The adjustment movement is supported by the hydraulic oil-pressurized pistons 20, 21 which act upon the eccentric rods 15, 16, wherein the pistons 20, 21 prevent a return of the eccentric adjustment mechanism 13 due to varying directions of action of the forces acting on the eccentric adjustment mechanism 13. The eccentric rods 15, 16 that cooperate with the pistons 20, 21 are connected with the eccentric body 14 on either side thereof. The hydraulic chambers 23 and 24, in which the pistons 20, 21 are guided, can be supplied with hydraulic oil via hydraulic oil lines 24 and 25 and from the crank pin bearing eye 11. Check valves 26 and 27 prevent a return flow off hydraulic oil from the hydraulic chambers 22 and 23 into the hydraulic lines 24 and 25. A bore 28 in the connecting rod 10 receives a switching valve 29 whose function is also already known from DE 10 2010 016 037 A1, with the switch position of the switching valve 29 determining which of the hydraulic chambers 22 and 23 will be filled with hydraulic oil and which of the hydraulic chambers 22 and 23 will be emptied, wherein the adjustment direction or the turning direction of the eccentric adjustment mechanism 13 depends thereon.
Fluid lines 30 and 31 respectively connect the hydraulic chambers 22 and 23 with the bore 28 that receives the switching valve 29. Of the switching valve 29, FIG. 1 schematically shows an actuation element 32, a spring element 33 and a control piston 34, the function of these components of the switching valve 29 being already known from DE 10 2010 016 037 A1.
As explained above, the hydraulic oil, which acts on the pistons 20, 21 guided in the hydraulic chambers 22, 23, is supplied to the hydraulic chambers 22, 23 from the crank pin bearing eye 11 via hydraulic lines 24 and 25, wherein the connecting rod 10 engages the crankshaft, not illustrated in FIG. 1, by the crank pin bearing eye 11 such that a connecting rod bearing shell 35 is arranged between the crankshaft, i.e. a crankshaft journal thereof, and the crank pin bearing eye 11.
According to DE 10 2010 016 037 A1, the control piston of the switching valve is adapted to be displaced or switched by a switching mechanism resembling a ball pen mechanism, wherein, besides the actuation element and the spring element, the switching mechanism preferably has a stationary detent element in the form of a control sleeve, and a turning element in the form of a turning sleeve. The spring element, the control piston, the turning element and the actuation element are all positioned one behind the other in the shifting direction of the control piston. The detent element surrounds the turning element and the actuation element at least in sections on the radial outer side. The switching valve therefore has a relatively long structure.